74 HOUSEHOLD BACTERIOLOGY 



caught in the twenty minutes' exposure shows the con- 

 dition in which uncovered jellies, puddings, sauces, 

 etc., are likely to be when placed in such places to cool ; 

 therefore, it is not c surprising that lemon jelly, jellied 

 meat, etc., are sometimes found in a liquid condition in 

 such a place. 



As we have said, some of the bacteria are capable 

 of liquefying gelatine. If the right species of bacteria 

 had happened to be present in the dust which settled 

 in this place, nothing could have prevented the gelatine 

 being liquefied, because the presence of the liquefying 

 bacterium would have been unknown until its work 

 had been done. A slight liquefaction is shown at the 

 largest spot in Fig. 46. 



The teacher who followed a lesson on the dangers 

 of dust by one on lemon jelly which she placed uncov- 

 ered in the open window to cool, did not apply the 

 scientific knowledge which she had. If she had done 

 as well as she knew, the contents of her mold would 

 have remained jelly and not become lemonade. 



